We are using Monday + BigQuery + DataStudio in order to get some proper statistics from our activity in Monday.
I set up a process that downloads items from specific boards (using the GraphQL api). I then take the response from that request and upload it to BigQuery as a table. I then query the table and create some views which expose the data I need in DataStudio. Then I connect DataStudio to these views and can make my reports.

I assume a similar approach would work for PowerBI. It is not the simplest solution, but is the only one I found to work that didn’t require writing a lot of code.

I’ve also created a NodeJS script and pushed it to Heroku to make it easier to import and format Monday items: https://github.com/Guichaguri/MondayPowerBIAdapter
It also generates a token that only gives access to a single board, so you don’t have to expose your API Key in your report. The key is stored in a database, but if you want you can take the code and host yourself.